1. Field of the Invention
The present invention relates to precipitated silicas having a high structure, to a process for the manufacture of the silicas and to the use of these silicas.
2. Description of the Background
The structure of a silica is understood to be the extent to which its primary particles congregate into secondary particles or, respectively, tertiary particles. The unit used to express the size of the structure is the Brabender dibutyl phthalate (DBP) absorption coefficient.
Spray dried precipitated silicas are known and sold, for instance, under the brand name of Sipernat®. The silicas are usually manufactured by precipitating water glass with sulfuric acid, wherein the entire width of possible precipitation variants can be deployed, as described, for example in EP 0 078 909, U.S. Pat. No. 4,094,771 or U.S. Pat. No. 6,013,234.
After precipitation the solid matter is removed by filtration and the filter cake is then spray-dried. If necessary, it is re-dispersed by adding an acid. Spray drying allows the manufacture of almost spherical, solid particles with a narrow size distribution range.
Silicas with DBP absorption values of up to 380 g/100 g are known as described in EP 0 078 909. In Example 1 of EP 0 078 909, a silica with 380 g/100 g DBP absorption value is obtained by spray-drying a silica suspension containing 11% solids by weight. According to Example 5 of EP 0 078 909 a DBP absorption of 346 g/100 g is obtained by spray-drying a silica suspension containing 16% solid matter by weight.
A similar process is disclosed in U.S. Pat. No. 6,013,234. In this case a silica suspension with pH>4 and a solids content of more than 18% by weight was spray-dried to form particles with an average particle diameter of more than 150 μm and a BET surface area of 100 to 350 m2/g.
The known spray dried precipitated silicas can be improved with respect to their DBP absorption values.